With the progress of the times, internet and mobile communication network provide a large amount of functional applications. A user can not only use a mobile terminal to perform a traditional application such as answering or calling using a smart phone, but also can use a mobile terminal to surf on a webpage, transmit pictures and play a game etc.
Since the using frequency of the mobile terminal is increasing, the mobile terminal needs to be charged frequently. In order to avoid security accidents caused by abnormal charging, a large amount of primary protection circuits are provided to prevent an over-charging and an over-discharging. However, if the over-charging or the over-discharging occurs, an existing primary protection circuit (including an over-charging and over-discharging protection circuit) switches off a charging loop or a discharging loop via a MOS transistor. Once the MOS transistor is broken down or damaged, the primary protection circuit will lose a protection function of preventing the over-charging and the over-discharging, thus causing electronic elements of the primary protection circuit being damaged, and causing other circuits inside the mobile terminal being damaged, and even causing a fire.